This invention relates to measuring and detecting coagulation and coagulation related activities in fluids, particularly human blood. More particularly, the present invention relates to improvements in apparatus used for measuring and detecting coagulation and coagulation related activities in human blood by different types of coagulation analytical tests, particularly those involving a plunger sensing technique.
There exist a number of different apparatus and methods for measuring and determining coagulation and coagulation related activities of blood. Examples of previous apparatus and methods which employ a gas flow sensing technique for performing certain types of coagulation related analytical tests are U.S. Pat. Nos. 4,752,449 to Jackson et al.; 4,663,127 to Jackson et al.; 4,599,219 to Cooper et al.; 4,534,939 to Smith et al.; 4,533,519 to Baugh et al.; 4,074,971 to Braun et al.; and 4,000,972 to Braun et al., all of which are assigned to the assignee of the present invention. Examples of previous apparatus and methods which employ a plunger sensing technique for performing certain types of coagulation related analytical tests are U.S. Pat. Nos. 4,599,219 to Cooper et al.; and 4,752,449 to Jackson et al., both of which are assigned to the assignee of the present invention.
Many previous techniques for accomplishing some or all of the coagulation and the coagulation related analytical tests are subject to variable results and inaccuracies because human variations in test procedures are introduced by the technicians conducting the tests and because some of the procedures for the tests. For example, measuring the amounts of blood samples to be tested must be accomplished manually, despite the use of automated equipment to perform the tests. Some manual analytical tests require relatively long periods of time to complete. In many clinical situations, it is desireable to conduct the coagulation related tests on a "STAT" (immediate) basis. It is, therefore, recognized as desireable to provide automated apparatus which can reliably and consistently execute analytical tests under consistent, reproducible and relatively rapid conditions.
Automated apparatus employing the plunger technique of measuring and detecting coagulation and coagulation related activities generally comprise a plunger sensor cartridge or cartridges and a microprocessor controlled apparatus into which the cartridges are installed and which acts upon the cartridge to induce and detect the coagulation related event. The cartridge includes a plurality of test cells, each of which is defined by a tube-like member having an upper reaction chamber where a plunger assembly is located and where the analytical test is carried out and a lower reagent chamber which contains a reagent or reagents. A plug member seals the bottom of a lower reagent chamber. The contents of the lower reagent chamber are forced into the reaction chamber to be mixed with the sample of fluid usually human blood or its components when the test commences. An actuator, which is a part of the apparatus, lifts the plunger assembly and lowers it, thereby reciprocating the plunger assembly through the pool of fluid in the reaction chamber. The plunger assembly descends by the force of gravity, resisted only by a property of the fluid in the reaction chamber. When a property of the sample changes in a predetermined manner, the descent rate of the plunger assembly therethrough is changed. Upon a sufficient change in the descent, the coagulation related activity is detected and indicated by the apparatus.
Although previous apparatus using the plunger sensing technique have proven generally satisfactory, the need for certain enhancements has been identified. The mechanical construction and elements used in prior apparatus have tended to create a level of ambient noise and mechanical vibrations and movement, which is undesirable in a clinical setting, and which may actually interfere with precise and sensitive detection of subtle but significant aspects of coagulation related activity. In prior apparatus such as that described in U.S. Pat. No. 4,599,219 a reagent drive subassembly forced upward the plug at the bottom of the reagent chamber to collapse the reagent chamber contents into the reaction chamber. This reagent drive subassembly was mechanically coupled to move in unison with a plunger lifting subassembly which lifts and lowers the plunger assembly. Since a relatively large amount of force is required to simultaneously force upward the plugs of a plurality of test cells in a cartridge, a relatively large motor is required. The relatively large motor limited the ability to obtain precise control over the rates and extent of movement of the plunger lifting assembly, particularly because of the relatively large amount of mechanical inertia associated with repeatedly reciprocating the elements of the reagent drive subassembly simultaneously with reciprocating the plunger lifting subassembly. Furthermore, it has been determined that many coagulation related tests may require independent control over the movement of the plug to collapse the reagent chamber contents into the reaction chamber and the movement of the plunger assembly at the commencement of the analytical test. This feature was, of course, impossible to achieve with the prior apparatus which mechanically linked the plunger lifting subassembly to the reagent drive subassembly for simultaneous movement.
The prior apparatus also required manual insertion and measurement of the fluid samples into each test cell. Because of human induced variances in the quantity of the sample introduced into each test cell, reliable and accurate results were only possible with relatively large blood samples of approximately 1.5 mL. Samples of a relatively large size were required because smaller samples could not be accurately measured by the technician, except with a pipetter. Experience has shown that in clinical settings, and particularly under STAT conditions, technicians will frequently choose to meter the sample into the cartridges by less accurate methods, such as with a syringe, thereby accepting inaccurate or incompetent test results, rather than utilize the time consuming method of pipetting the blood. The use of the larger sample size also reduced the variance in test results introduced because of the variance in the sample size, because the degree of sample size variance could be reduced relative to the size of the sample. Larger sample sizes also require larger cartridges for some tests and greater quantities of reagent, thereby increasing the cost of the cartridges. Sometimes, the larger sample size made the finer and more subtle coagulation related changes more difficult or impossible to detect. The need to use large sample sizes requires larger quantities of blood to be collected from the patient, and/or reduces the quantity of blood which might be available for other medical tests.
It has been determined, therefore, as advantageous to improve the prior art coagulation detection apparatus to overcome these and other difficulties and undesirable effects. It is against this background that significant improvements and advancements have evolved.